Electron magnetic chiral dichroism in CrO2 thin films using monochromatic probe illumination in a transmission electron microscope

Electron magnetic chiral dichroism (EMCD) has been studied in CrO2 thin films (with (100) and (110) growth orientations on TiO2 substrates) using a gun monochromator in an aberration corrected transmission electron microscope operating at 300 kV. Excellent signal-to-noise ratio is obtained at spatial resolution similar to 10 nm using a monochromatic probe as compared to conventional parallel illumination, large area convergent beam electron diffraction and scanning transmission electron microscopy techniques of EMCD. Relatively rapid exposure using mono probe illumination enables collection of EMCD spectra in total of 8-9 min in energy filtered imaging mode for a given Cr L-2,L-3 energy scan (energy range similar to 35 eV). We compared the EMCD signal obtained by extracting the Cr L-2,L-3 spectra under three beam diffraction geometry of two different reciprocal vectors (namely g=110 and 200) and found that the g=200 vector enables acquisition of excellent EMCD signal from relatively thicker specimen area due to the associated larger extinction distance. Orbital to spin moment ratio has been calculated using EMCD sum rules for 3d elements and dichroic spectral features associated with CrO2 are compared and discussed with XMCD theoretical spectra. (C) 2012 Elsevier BY. All rights reserved.